The present invention relates to an ink-jet printer of the type wherein the velocity of an issuing ink drop is controlled depending upon a given point of a dot matrix where the ink drop is deposited.
In the prior art charge variable, deflection type ink-jet printers, the pressurized ink is supplied to an ink drop generator or an ink manifold on which is mounted a piezoelectric crystal so as to cause a pressure vibration of the ink in the ink manifold. The ink jet emerging through a nozzle of the ink drop generator breaks into ink drops in a charge electrode and the charged ink drops are deflected by a pair of deflection electrodes so as to be deposited at given positions on a recording medium.
The deflection of a charged ink drop on a recording paper from the axis of the nozzle of the ink drop generator is given by ##EQU1## where
Qj=charge on an ink drop;
mj=mass of an ink drop;
Vd=deflection voltage;
Sd=distance between the deflection electrodes;
vj=velocity of an issuing ink drop;
ld=length of the deflection electrodes; and
Zp=distance between the inlet surface of the deflection electrodes and the recording paper.
The prior art charge variable, deflection type ink-jet printers are based upon the fact that the deflection of an ink drop is in proportion to the charge Qj on that ink drop as shown in Eq. (1). That is, the charge imparted to each ink drop is controlled in response to the drop-placement signal; consequently, each charged ink drop is deposited at a given position on the recording paper. Therefore the deflection is dependent upon the charge on each ink drop.
The ink-jet printer of the type described must be therefore provided with a means for varying the charge to be imparted to an ink drop depending upon a given position in a dot matrix at which the charged drop is to be placed. In addition, the ink-jet printer needs a pump for pressurizing the ink and a means for detecting the phase at which the ink jet breaks into a stream of ink droplets.